The present invention is a method for forming blends of polydiorganosiloxanes and solid, sulfonated polyolefins and novel blends prepared by the method. In the present method a solid, sulfonated polyolefin is swollen with a diorganosiloxane oligomer whose rearrangement to high molecular weight polydiorganosiloxanes is catalyzed in situ by the sulfonic acid substituents of the polyolefin.
Incorporation of a polymer inside another polymer matrix is a useful technique for preparing a material with a different set of properties than either of the individual polymeric components. Such a multicomponent system can be prepared by swelling a polymeric matrix with a monomer which is then polymerized and crosslinked in situ. The poor miscibility of diorganosiloxanes with most organic polymers has impeded their use in such multicomponent systems.
The present inventors have found that the sulfonic acid substituents of solid, sulfonated polyolefins can serve as an in situ polymerization catalyst for diorganosiloxane oligomers diffused into the matrix of the solid, sulfonated polyolefin. Depending upon the concentration of polydiorganosiloxane present in the multicomponent system, the polydiorganosiloxane can be present as an interpentrating network, a pseudo-interpentrating network, or as isolated domains within the matrix formed by the sulfonated polyolefin. Blends prepared by the present method can have improved and unique properties when compared to the solid, sulfonated polyolefin.
The acid-catalyzed rearrangement of siloxane linkages in organopolysiloxanes is a well known reaction. For example, Hurd, J. Am. Chem. Soc. 77:2998, 1955, describes the use of sulfuric acid to catalyze the rearrangement of octamethyltetracyclosiloxane to high molecular weight linear polydimethylsiloxanes. A similar process is described by Koshima et al., Nippon Kagaku Zasshi, 77:1755-1759, 1956.
Finke et al., U.S. Pat. No. 4,310,679, issued Jan. 12, 1982, describe a process where an organosiloxane mixture is equilibrated by contact with a cation exchange resins which has side chains carrying sulphonyl groups, the carbon atoms carrying the sulphonyl groups also carrying at least one fluorine atom.
In addition, it is known in the art to improve the properties of materials such as chlorosulfonated polyethylene by the incorporation in the composition of other polymeric materials. For example, Watanabe, Japanese Kokai Patent Application No. Hei 3(1991)-139545, describes a process where a chlorosulfonated polyethylene is blended with a an alicyclic epoxy compound. The cured composition is reported to have improved fatigue resistance, when compared to the chlorosulfonated polyethylene.
Densen et al., Japanese Kokai Patent Application No. Hei 2(1990)-242839 describe a process where a liquid chlorosulfonated polyethylene is blended with a liquid siloxane mixture containing silicon-bonded hydrogens and vinyls that can undergo a hydrosilation reaction in the presence of a platinum compound. Crosslinking of the liquid siloxane or both the liquid siloxane and the chlorosulfonated polyethylene is effected to form a macromolecular network structure.
The described art does not recognize that a solid, sulfonated polyolefin can act as a catalyst for the in situ polymerization of polydiorganosiloxane oligomers to form high molecular weight polydiorganosiloxanes within the matrix of the solid, sulfonated polyolefin. In the present method the problem associated with the miscibility of polyorganosiloxane polymers with olefins is largely overcome. In addition, no fugitive catalyst is present in the composition that must be removed by additional processing. The in situ polymerization of the diorganosiloxane oligomers in the matrices of the solid, sulfonated polyolefin can provide for improved physical properties of the sulfonated polyolefin.